The measurement system developed at NPL using NIST (formerly NBS) designed Josephson junction arrays as the UK means of realising the volt is described. This system is regularly used for measurements of commercial Zener references and has also been used to measure standard cells directly, with a standard error of the mean of nine measurements on a standard cell of 0.15 nV. The use of the Josephson junction array system for measurements on resistive voltage dividers (RVD) is also described. RVD ratios have been determined by voltage measurements at pairs of divider terminals and their ratio calculated. This method is compared with more traditional ones.